Loud HVAC

[michaell1999]

My HVAC air intake is located on a wall in my living room.
The HVAC itself is located very close to this intake. There is about 2feet from the grill on the wall to the air filter. The HVAC is right next to the air filter.
It looks like the builder lined the inside of the air intake with a 1" thick insulation. Removing the grill and filter does nothing to reduce the noise. The fan speed is at the low setting. The noise isn't from air movement but the HVAC motor.

I was thinking of applying Dynamat to the outside of the HVAC sheetmetal.

Any other suggestions?

Thanks

 

[MDS]

I have a similar situation and the noise pollution is slowly driving me crazy.

I bought some sound dampening sheets from PartsExpress (similar in concept to DynaMat but not metallic and also UL rated against fire). I put the sheets over all of the walls of the enclosure and on the walls of the air handler. It helped a little. I also placed 2" thick acoustic tiles in the enclosure and that also helped a little.

The SPL measurement is actually 10 dB lower than it used to be but still nowhere near acceptable. I think the only real solution if your HVAC is similar to mine (and it sounds like it) is to tear down the wall and rebuild it with two layers of drywall separated by Rockwool or some other insulator. That's going to make it to the top of my 'to do' list real soon.

 

[WmAx]

On top of MDS's radical suggestion, you may also require a special baffle junction that reduces noise from one section of the ducting to the next. It is essentially a huge 'muffler'; it attenuates broadband sound from entrance to exit of the duct where it is installed. These are commonly used in major installs where acoustically isolated sound rooms are installed. But you may not need to take down the original wall. Just make sure it's air tight, fill the space between studs with thick insulation, and install a second drywall layer on the back of the first wall, but don't attach it to the original studs. Put up new studs and install the 2nd, inner drywall layer to these, and make sure this is air tight as well. The ducting isolation baffle will be needed. But if you combine these two things, this should prevent the majority of noise from entering, unless you also have noise coming out of the exit ducts. Of course, my suggestion also depends on you having sufficient access to the other side of the wall and having space to install the isolation ducting system.

If you have noise breach from the HVAC from other rooms entering the sound listening room, you may even have to encapsulate the HVAC system in a noise reduction shell. This involves building a noise isolation barrier all the way around the HVAC unit and then using acoustic duct isolation baffles for all entering/exiting air paths to the HVAC. This is done in extreme circumstances sometimes.

My central A/C is very loud, and on the same wall as my listening room. The noise comes right through from outside. So I simply do not turn it on when listening. To cool the listening room, I installed a window AC in a room beside my listening room. I mounted the A/C unit on a special vibration de-coupling suspension to prevent vibration from going through the wall physically. I then ran insulation lined flex ducting through a wall to a closet, crossing the length of it, then folding back and feeding a vent to the listening room. This acts as an acoustic isolation baffle. I also have a return air passage similarly installed. This gave me extremely silent A/C for my listening room.

-Chris

 

[Savant]

Mass-loaded vinyl, or MLV (Dynamat), around the blower casing will not help if the sound is primarily coming through the vent. Also, with only 2 feet between the blower and the vent, there's not much to work with. Even something like Chris is suggesting might have limitations being located so close to the blower intake. It all depends on how relatively "straight" such a construction can be. Acoustical duct treatments work best if the air has several duct diameters of straight run before encountering any transitions. A plenum such as Chris described still needs to have a fairly straight run for the airflow when it is so close to the intake. If such a construction (again, so close to the intake) becomes too zig-zaggy, it may attenuate blower noise, only to replace it with turbulent airflow noise. (Not to mention that it might have a negative impact on blower performance / efficiency.)

What I would suggest, if there is space available, and assuming the intake is located high on the wall (as they often are), is to run a acoustically-lined duct clear across the room. This need not be the same dimensions as the air intake, but should have roughly the same (or larger) cross-sectional area. For example, if you have a 24"x24" intake, a duct that runs across the ceiling that's 10" high x 60" wide would work. Each linear foot of acoustically-lined duct will attenuate roughly 3-5 dB of broadband sound (with less attenuation at low frequencies; more attenuation at high frequencies). An opening on the opposite end of the duct - now many feet away from the intake - will still pull the right amount of air into the unit, but with much less noise.

There are other approaches. The performance of anything will depend on how much sound is coming out the vent (probably a lot, relatively) versus what's coming through the wall. There might be a point where the vent / duct noise is attenuated to a point where the noise coming through the wall becomes the annoying part.

FWIW, there is a good write-up on HVAC noise located here. (I developed much of it back when I worked for Auralex.)

 

[Rickster71]

I just replaced our attic HVAC & air handler, it was 17-years old.
The large intake vent, was just outside of our bedroom door, when the unit cycled on it would always wake me up at night.

Our new replacement unit is so quite, that I can't tell that it's on until I feel the room getting cooler.

If your HVAC is over ten years old, give some consideration the replacing it. A new one will be more energy efficient also.

 

[michaell1999]

Thanks for the suggestions.

My HVAC is 4 years old. It is a Lennox Merit model with a 1/2 hp motor.

I'll try to post a pic of the layout.

 

[mtrycrafts]

Thanks for the suggestions.

My HVAC is 4 years old. It is a Lennox Merit model with a 1/2 hp motor.

I'll try to post a pic of the layout.

While I read through much of the posts, I didn't see a mention about the doors to the closet. That should be air tight and solid core, perhaps the inside also faced with acoustic absorption material.

 

[michaell1999]

The door is not solid core but it is sealed tight with a heavy duty sweep and foam around the door. The door is on the other side of the living room.

 

[michaell1999]

Picture of the air intake with grill removed. You can see the air filter in back. Right next to that is the HVAC.

 

[mtrycrafts]

Picture of the air intake with grill removed. You can see the air filter in back. Right next to that is the HVAC.

Boy, that will be tough to quiet down. When it is on, what is the spl reading say 1ft into the room? I bet a lot of the noise comes through that opening.

Remodel the house for radiant heat Super quiet I don't hear mine

 

[Soul Shinobi]

I've been reading on sound deadening for PCs and came across an article on Silent PC Review about the anechoic chamber they made. There were some materials noted, particularly QuietRock sound deadening drywall (the maker, Quiet Solutions has a lot of different products) and UltraTouch Cotton in wall insulation. Also there are several sound deadening products for sealing the cracks where drywall boards meet, and covering the backs of electrical outlets. Hope those links help! I'm currently working on a sound deadening topic in this subforum.